We describe a new tool, BIG-MITgcm, that consistently reproduces the global-scale dynamics of the ocean, atmosphere, vegetation and ice on multimillennial timescales at a low computational cost. Evaluated against observations and state-of-the-art Earth system models, it includes asynchronous coupling to models of vegetation, hydrology and a newly developed global-scale ice sheet. Using arbitrary continental configurations, it enables studies of past and present climates on Earth or exoplanets.